Date controls should respect user time preferences

Summary: Ref T8362, Date controls should respect user time preferences

Test Plan: Set user time preference to 24-hour format, create an event, type 23 in time input, 23:00 should be suggested. Saveing a 24-hour format time should save correctly.

Reviewers: #blessed_reviewers, epriestley

Reviewed By: #blessed_reviewers, epriestley

Subscribers: epriestley, Korvin

Maniphest Tasks: T8362

Differential Revision: https://secure.phabricator.com/D13291